EH researcher maps city noise

Driven to distraction by her noisy apartment building, US environmental health student Erica Walker thought it worthy of further investigation. While she could block out the sound of running footsteps in the apartment overhead, she could still feel the thumps of each step in her body.

It was this sound component that interested Walker and so the environmental health PHD student, at Harvard T.H. Chan School of Public Health, decided to look into infra noise and low frequency noise.

She said: ‘It’s like supernoise. If there’s something that’s high pitched and you want to get away from it you can put your fingers in your ears and you can severely abate it. But this low frequency noise is outside of the auditory system and you can’t escape it. It is being sensed by other organs. It’s really unwanted because there’s nothing you can do about it.’

An example of low frequency sound is a bus (which is very low but can still be heard) but there is also an infra sound component, as the rumbling of the bus is also felt by the body.

Examples in nature of infra sound, or vibrational sound, are earthquakes and volcanoes. So there is a question around how the body has evolved to react to these sounds considering that in nature they relate to dangerous natural events.

To answer some of these questions Ms Walker has been cycling all over Boston with recording equipment to map the different levels of sounds of the city. She will share her findings at the conference NoiseCon 2016 in June in Providence city, Rhode Island.

Ms Walker is also contributing to a study examining the cardiovascular effects of low frequency noise. The paper will be published in Environmental Research and does indicate that low frequency noise has a negative impact on heart rate variability.

Ms Walker said: ‘Low frequency noise has an impact on – above and beyond – high frequency noise on short term cardiovascular activity. Over a period of time how this is manifested over ten or 20 years we don’t have any answers but that’s where we need to gear our future research.’

Infra sound sits in the category 0-20 hertz, while low frequency sound sits in the category of between 20-150/200 hertz. The WHO has set guidelines on high frequency noise at 55 decibels during the day and 45 decibels at night. Ms Walker’s research is showing that these guidelines are often being exceeded by 15-20 decibels routinely. However, there are currently no guidelines on low frequency noise.

She said: ‘The WHO organisation has identified it as an issue that needs to be addressed for the future. This part is able to seep in after we’ve done something to keep the noise out. It’s something that needs legislation.’